Batteries such as alkaline storage batteries and lithium ion secondary batteries are widely used as the power source for portable devices, machine tools, or electric vehicles. Of these, nickel metal-hydride storage batteries have a relatively high energy density and excellent durability, and the applications thereof, including as power sources for electric vehicles, are being expanded.
Generally, the main components of nickel metal-hydride storage batteries include: a positive electrode formed by filling a three-dimensional metal porous material with nickel hydroxide and other materials; and a negative electrode formed by applying an electrode mixture paste composed of a hydrogen-absorption alloy and other materials to porous metal thin plate (hereinafter simply abbreviated as a “core material”) such as a punched metal. Of these two, the negative electrode can be produced continuously because of the nature of its production process, which has received attention as a highly efficient process. Specifically, a method has been proposed in which, after the core material is immersed in the electrode mixture paste, the application amount of the electrode mixture paste is adjusted to produce a paste-coated sheet.
As a method for drying a paste-coated sheet, a method is exemplified in which a paste-coated sheet is made to continuously travel through a drying furnace which generates hot air or far infrared radiation. In terms of improving the ease of conveyance of a paste-coated sheet and space saving, a method is often employed in which a paste-coated sheet is brought into contact with rollers provided at several positions, so that the traveling direction is changed by approximately 90 degrees. In this method, traveling stability is high since a suitable tension can be applied between the rollers, and the space in the height direction can be utilized. Accordingly, it is conceivable to realize a drying step excellent in space efficiency.
However, when a paste-coated sheet in a wet state is brought into contact with a flat roller, the electrode mixture paste is transferred thereto. Hence, insufficiently dried portions of the paste-coated sheet are brought into contact with wheel type rollers as shown in FIG. 6. When an electrode mixture paste is actually applied and dried utilizing such wheel type rollers, generally, the electrode mixture paste is removed from both edge portions in the width direction of a paste-coated sheet to provide core material-exposed portions, and the paste-coated sheet is made to travel while the core material-exposed portions are clipped (see, for example, Patent Document 1).
[Patent Document 1] Japanese Patent Laid-Open Publication No. 9-017420